Based on a fluid dynamical concept of the mechanics of the pleural space, it is proposed to calculate the time history and spatial distribution of pleural pressure, and stress on the lungs, under a variety of conditions. These will include stationary and moving chest wall and diaphragm, and upright, supine and inverted positions. As a direct aid to the theoretical work, model experiments are proposed to elucidate the geometrically complicated distributions. Concurrently, measurements of pleural pressure distribution in dogs is proposed, under apneic, forced breathing and voluntary breathing conditions. The emphasis will be to obtain a unified dynamical picture of pleural space mechanics. With this dynamical picture on hand, it is proposed to investigate the coupling of the pleural space mechanics with the lung mechanical structure, and the distribution of gas in the lungs under different breathing patterns. With the growing effort to develop diagnostic procedures which account for non-uniformities of gas distribution in the lungs, and to infer lung mechanical properties from external measurements, it becomes increasingly necessary to obtain this dynamical information.